Notes:

After I'd finished my Yuletide assignment I thought I'd write a treat and the prompt for a NBX/Discworld crossover caught my eye. I'd never written in these fandoms before, but they're two of my favourite Christmas themed media, and once the similarities were pointed out by the recipient I couldn't resist.

"Now that we've established that you are not my grandfather, but someone called Jack Skellington, let's return to my original question. Where is my grandfather?"

A gigantic skeleton ought not to be fearful of an average sized human girl, but a combination of Discworld genetics, school teacher training and a term of service as a governess gave Susan Sto Helit quite the advantage here. Her stare could have demi-gods apologising for the mess and promising to clean up after themselves. The Voice, a true manifestation of her heritage, could probably have gods sending her fruit baskets and throwing meteor showers in her honour.

"He's in Halloweentown."

"Which is what? Your world?"

Jack nodded and said in a small voice, "'es."

"Excuse me? Speak up."

"Yes," Jack said, finally meeting her gaze with his hollow eye sockets. "Where it is Halloween every day and we plan to bring our fun to the people of Earth once each year."

"And what, precisely, is Halloween?" Susan could hear the Death of Rats behind her, giggling. She studiously ignored him.

"A holiday," Jack explained, bony arms flung wide in delight.

"And what do you celebrate, exactly?"

Jack seemed to frown. His skull was more expressive than her grandfather's. "We have fun scaring people," he said. "It's a time when the veil between worlds is at its thinnest."

"That sounds like a recipe for disaster rather than a holiday," Susan said sternly. In the corner of her eye she could see the raven, head tucked under one wing in an unsuccessful effort to hide his amusement.

Jack brightened up as something occurred to him. "But we have songs! Like this:

what's this, what's this, a clever talking birdwhat's this, a rat without his furwhat's this, a girl who says that -

Jack stopped singing abruptly, mostly because Susan had grabbed the scythe he'd left propped up against the dresser, and tripped him up with the wooden handle.

"Oof," Jack said. He was heap of long, tangled limbs. With difficulty, he righted himself.

"This is a scythe," Susan said. "Death's scythe. You shouldn't leave it lying around. It cuts through anything."

"Anything?" Jack asked. He took half a step backwards.

"Anything," Susan said grimly. The blue edged of the scythe glimmered a moment as if responding to this praise. "So, this Halloween. It involves Otherworldly creatures terrifying normal people while you stand around singing songs about it?"

"Yes! Only you make it sound so wrong," Jack complained. "And I just don't stand around." He puffed up and posed dramatically. "I am the Pumpkin King!"

It seemed unlikely, but being Death's granddaughter had given Susan a rather unusual perspective regarding the unlikely, the improbable and the plain impossible. "Go on."

"Well, we have so much in common," Jack said.

"Like being walking skeletons," the raven put in, despite this earning him a glare from Susan.

"Yes. And we've both taken the place of the personification of the Christmas spirit who I know as Sandy Claws and you know as the Hogfather. Large man," Jack said helpfully, "wears red, delivers presents to good girls and boys."

Susan raised one eyebrow. "You have both impersonated a wintry, gift giving, demigod?"

"Yes! What are the chances?"

Better than he might have imagined. It was that damn narrative causality again, Susan thought sourly. No matter how obscure or odd a story might seem, having being told once, it would seek to replicate itself over and over, echoes of it rippling out across the multiverse.

"And in one of Grandfather's harebrained schemes, he asked you to switch places with him?"

"Just temporarily...he has a hare brain?" Jack asked, fascinated. "Does it jump around in his skull?"

"Never mind that," Susan said with a sigh. "So, you're here doing grandfather's job." Not as if there was anything that could possibly go wrong with this scenario!

Jack scratched at his skull. "I'm trying to, yes. Is there perhaps an instruction manual? I've been looking for someone to advise me - we have a mayor and a renowned scientist in Halloweentown, but there seem to be so many people in your world who think they're in charge, and -_"

Susan held up a hand for his silence. "Your job is to collect souls. Not all of them, of course, but certain ones." What she wasn't about to tell Jack "The Pumpkin King" Skellington was that she wasn't certain of all the details herself. There were the timers, whose sand measured out the lifetimes, and there was the scythe that was used for slicing a soul from the body, and of course there was Binky who knew way too much for a horse in Susan's opinion. And of course there was the Death of Rats - who was still enjoying this charade immensely. She knew that witches and wizards and kings had to be personally collected by Death himself, but there had to be a lot more to it than it. An instruction manual? It was an intriguing idea.

"I'll see what I can do," she said, resigned. Because she was Death, if He was unavailable, and so whether she helped Jack muddle through or stood by and let him fluff it up so badly she finally had to assume the mantle herself, it was all pretty much the same thing. The best she could hope for was that no idiot wizard used the Rite of AshkEnte to summon Death until she got the real one back. News of an impostor working as the Grim Reaper would only cause panic.

"Now, while you're here -"

"Can we go sightseeing?" Jack begged. "I hear you have some lovely zombies and witches."

Lovely wasn't the word Susan would use for any zombie, not even the fairly pleasant ones. And Jack might find himself in big trouble if he tried singing at witches. Granny Weatherwax had no truck with that sort of thing.

"Maybe later. But Jack, what about my grandfather? What's he doing?"

Jack beamed widely. "Why, my job of course! Pumpkin King. He took his little friend with him and I told Sally to look after them. She's very sensible."

I'll bet she is, Susan thought. Behind every unthinking male's stupid plan was a woman picking up the pieces. That thought was far more comforting than the fact that Albert had gone with grandfather.

Albert shook his head grimly. "Master, can't we go home?"

NOT YET, ALBERT. I THINK I'M GETTING THE HANG OF THINGS NOW.

"You should see what's in the fridge, master! Some it's still wiggling!"

MAYBE LATER.

Death looked up from the scrolls. They were Jack's plans for the next Halloween celebration. Death had the vague idea that Halloweentown was a bit like a Guild of Monsters, a sort of Biers that encompassed a whole town rather than a bar. Everything from zombies and witches to boogeymen and vampires lived here quite peaceably, under the supposed auspices of the mayor and under the actual authority of Jack Skellington and his girlfriend, Sally.

Albert glared at Death, but the master wasn't paying him any attention. Albert would starve to death here - well he would, if he wasn't sort of undead and this world obeyed any sort of physical rules. The holiday worlds were not exactly part of the real world, so Albert could exist here. He was beginning to wish that were not the case.

This is Halloween, Halloween, Halloween

The song drifted in through the window. Albert had heard that song three times already this morning and it was getting on his nerves. He didn't like this place at all. Despite the overall similarities between Jack and Death, things here were just not right.

The trick or treaters (tricky buggers, more like) had snuck in and stolen his packed lunch. The twofaced mayor had been round to meet Jack, with his smiley face showing - and left with his monstrous one on. And Death was trying to implement Jack's bizarre notions of fun—they seemed to consist largely of creatures hiding under things and jumping out at unsuspecting people.

There was no Halloween on the Discworld, (aside from that Soul Cake Duck business) and Albert was very glad of that. He couldn't imagine Mr Slant, the foremost legal mind on the Disc, and a long-time zombie, bursting into song and dancing around the courtroom the way these creatures did. The only mercy was that Susan was bound to find out and come and put things right. Any moment now.

"Here's some absinthe," Sally said brightly, handing Albert a glass.

He shrugged and downed it in one go. Not like it could kill him, not here where everyone was already dead. "Got any mince pies?"

"We have candy," she said uncertainly.

Albert grunted in agreement. Absinthe and candy would have to tide him over until Susan showed up.